SJC Land

Two-phase neighborhood evaluation

Assign every residential parcel to a neighborhood

Given that neighborhood structure

  • Develop trending factors for each neighborhood with more than 3 or 5 sales

  • Separate trending factors are estimated for land and improvement

Apply the trending factors and evaluate:

  • The resulting ratio and COD

  • The percentage of properties trended

  • Repeat for each of the five years 2013-2017

Repeat for each classification scheme

  • Current neighborhoods, townships, school districts, census tracts, etc.

  • Further division based on clustering by acreage, year built, sq. ft., # of rooms

Describe tradeoffs between the different classifications tested.

2017 Sales

Initial Model

For an initial pass, we construct a model in which valid sales prices were predicted by land and improvement values. The values taken from this baseline model were then used to calculate updated assessed values.

Base Results
COD 12.986829
Ratio 1.008983

With a very basic model, we were able to achieve reasonable values on both COD and Ratio.

Existing Neighborhood Results

As a next step, we computed individual regressions for each pre-existing neighborhood with at least 5 sales.

Min = 5

Neighborhood Results
trueCOD 11.2130345
ratio 1.0040836
proportion 0.7210493

Min = 3

Neighborhood Results
trueCOD 11.0237743
ratio 1.0041818
proportion 0.7924216

School Districts

Min = 5

School District Results
trueCOD 12.966301
ratio 1.004886
proportion 1.000000

Min = 3

School District Results
trueCOD 12.966301
ratio 1.004886
proportion 1.000000

Tax Districts

Min = 5

Tax District Results
trueCOD 13.4511233
ratio 1.0225523
proportion 0.9819206

Min = 3

Tax District Results
trueCOD 13.4542618
ratio 1.0224384
proportion 0.9884329

Township

Min = 5

Township Results
trueCOD 13.6441386
ratio 1.0204829
proportion 0.9972428

Min = 3

Township Results
trueCOD 13.6441386
ratio 1.0204829
proportion 0.9972428

Tract

In an attempt to find an additional way to create neighborhoods, we also used Census Tracts.

Min = 5

Tract Results
trueCOD 12.6603262
ratio 1.0092367
proportion 0.7743947

Min = 3

Tract Results
trueCOD 12.6464636
ratio 1.0092221
proportion 0.7866446

Combined

After examining individual geographical areas, we made an effort to nest geographical features into two levels.

School District & Township

School District & Township Results
trueCOD 13.6027716
ratio 1.0198828
proportion 0.9972428

Township & Tax District

Township & Tax District Results
trueCOD 13.4511233
ratio 1.0225523
proportion 0.9819206

Tax District & Tract

Tax District & Tract Results
trueCOD 12.5715277
ratio 1.0098171
proportion 0.8331758

Clustering

Given the relative performance of tract, an effort was made to break the homes within tract into discreet clusters. The features selected clustering were acreage, year built, finished dwelling area and finished rooms. For each individual school district or tract, 2 distinct clusters were created.

School District Clusters

School District Cluster Results
trueCOD 12.9986636
ratio 1.0042643
proportion 0.9913214

Tract Clusters

Tract Cluster Results
trueCOD 12.0229593
ratio 1.0083396
proportion 0.7122525

Mixed Models

Instead of fitting models to individual groupings, we also tried a mixed model in which every tract X cluster combination has its own slope within the model.

Base Results
COD 10.597028
Ratio 1.009745

Previous Years

Given the reasonable results of the tract X cluster combination, we can see how it performs over the previous years.

2016

Township Results
trueCOD 14.3687358
ratio 1.0417522
proportion 0.9972347
Neighborhood Results
trueCOD 10.7265009
ratio 1.0021303
proportion 0.6956888
Tract Results
trueCOD 12.3242613
ratio 1.0045554
proportion 0.7119249

2015

Township Results
trueCOD 12.8624315
ratio 1.0187185
proportion 0.9972983
Neighborhood Results
trueCOD 10.2757028
ratio 1.0024316
proportion 0.6486864
Tract Results
trueCOD 11.8786006
ratio 1.0045146
proportion 0.6678112

2014

Township Results
trueCOD 12.0910325
ratio 1.0269729
proportion 0.9972973
Neighborhood Results
trueCOD 9.092055
ratio 1.001457
proportion 0.629402
Tract Results
trueCOD 10.4149531
ratio 1.0034560
proportion 0.6213207

2013

Township Results
trueCOD 16.8158823
ratio 1.0283018
proportion 0.9910053
Neighborhood Results
trueCOD 10.7369317
ratio 0.9971802
proportion 0.5721526
Tract Results
trueCOD 12.0105377
ratio 0.9939950
proportion 0.6179198